1. Field of the invention
This invention relates in general to connectors for pipe of large diameter used in offshore drilling operations, and in particular to a method for testing pipe connectors of a snap type which connect together by a straight compressive force.
2. Description of the Prior Art
During initial stages of drilling an offshore subsea well, large diameter pipe will be used for various purposes, such as risers and conductor pipe. The pipe may be 20-30 inches in diameter, with each section being about 40 feet long. The connectors between each pipe section must handle high tensile forces, and also be able to accommodate bending moments. Making up the joints is difficult, particularly on floating vessels which have wave motion, currents and wind.
U.S. Pat. No. 4,601,491, Jul. 22, 1986, James L. Bell, Jr., et al., discloses a connector that has mating conical profiles formed in box and pin members. The profile utilizes a thread form with grooves and crests which stab straight inward under compressive force. During insertion, the profiles of the box and pin will interfere with each other radially in an intermediate position until sufficient compressive force is applied to overcome the frictional force due to the radial interference. Once this is overcome, the crests will snap into the grooves, forming the connected position. Radial interference exists in the connected position, also, however to a lesser degree than in the intermediate position.
The apparatus for snapping the pipe connectors together is a large clamp tool. The clamp has an upper clamp ring that engages an external groove on one connector, and a lower clamp ring that engages an external groove on the other connector. Hydraulic cylinders extend between the upper and lower rings. When actuated, the hydraulic cylinders will pull the rings toward each other to exert the compressive force to make the connection.
Once the connectors appear visually to have snapped into the locked position, the clamp rings are radially retracted and the sections of pipe lowered until the next connector is reached. In the prior art, checks are made to ensure that the gap between the two external faces of the connectors is less than a specified dimension. Also, the circumference of the box connector is measured before and after makeup. This provides an indication as to the state of the makeup.